In vitro activity of Ro 15-8074 and Ro 19-5247, two orally administered cephalosporin metabolites

The activity of two iminomethoxy aminothiazoly cephalosporins, Ro 15-8074 and Ro 19-5247, was compared with that of other beta-lactams against a total of 491 bacterial strains. Both were highly active (MIC for 90% of the strains tested [MIC 90], less than or equal to 2 micrograms/ml) against the majority of the members of the family Enterobacteriaceae, Haemophilus influenzae, Neisseria spp., and Streptococcus pneumoniae, being at least 16-fold more active than cephalexin and 8-fold more active than cefuroxime. There was no activity against Pseudomonas aeruginosa and poor activity against Morganella morganii (in the case of Ro 15-8074), Enterobacter sp., and Citrobacter sp. Staphylococcus aureus was moderately susceptible to Ro 19-5247 (MIC90, 8 micrograms/ml), but Ro 15-8074 was eightfold less active. The protein binding of the two compounds at 5 micrograms/ml was 9.1% for Ro 15-8074 and 69.9% for Ro 19-5247. The major target site for the two cephalosporins was PBP 3.